re-entry visa

Hi,

Does anybody know how the re-entry visa works?

Where is it possible to apply for a re-entry visa? At any border check point, when leaving Vietnam? And can you get one imidiately?
And what about the visa expiricy date. If you have a 30 days visa, and leave Vietnam for 15 days, will those 15 days count, or will the visa expiricy date be postponed 15 days?
And price? Any idea?

And just a quick question about the regular visa: The 30 days of o '30 days visa' start to count the day you enter Vietnam, is this right?

Cheers

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